A British Muslim activist who was found guilty of willfully obstructing police by a UK court after he refused to hand over his mobile phone and laptop computer's pin number, says he is going to appeal against the decision.

Muhammad Rabbani, 36, was arrested at London’s Heathrow airport last November and was charged six months later with obstructing police.

"I will be appealing this decision," Rabbani who is the international director of CAGE - an organisation which provides legal advocacy for those affected by British terrorism legislation - said in a statement on Tuesday.

"This judgement confirms that a person can fall foul of terrorism laws for protecting client confidentiality. The principle of presumption of innocence, the principle of client confidentiality and the principle of personal privacy are all too important to surrender even with the threat of conviction."

Rabbani was held under Schedule 7 of the Terrorism Act, which gives police a broad range of powers to search individuals at ports of entry without grounds for suspicion.

He said he refused to hand over the gagdet to police because they contained sensitive information from an alleged torture victim of US security agencies.

Rabbani was ordered to pay court costs of $707 and was granted a conditional discharge of 12 months.

"This is a mockery of the concept of due process - the exercise of a principled, rational, truthful, justifiable concern that legitimate confidential obligations should be respected is transformed instead into a strict liability criminal offence," Gareth Peirce, Rabbani's lawyer, said.